1. Field of the Invention
The present invention relates to a method for making a thermionic electron source adopting carbon nanotubes.
2. Discussion of Related Art
Carbon nanotubes (CNT) are a carbonaceous material and have received much interest since the early 1990s. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties. Due to these and other properties, CNTs have become a significant contributor to the research and development of electron emitting devices, sensors, and transistors, among other devices.
Generally, an electron-emitting device has an electron source using a thermal or cold electron source. The thermal electron source is used by heating an emitter to increase the kinetic energy of the electrons in the emitter. When the kinetic energy of the electrons therein is large enough, the electrons will emit or escape from the emitters. These electrons emitted from the emitters are thermions. The emitters emitting the thermions are named thermionic emitters.
Conventionally, the thermionic electron source includes a thermionic emitter and two electrodes. The two electrodes are located on a substrate. The thermionic emitter is located between two electrodes and electrically connected thereto. The thermionic emitter is generally made of a metal, a boride or an alkaline earth metal carbonate. The thermionic emitter can be divided into two types, a direct-heating type and an indirect-heating type. The thermionic emitter of the direct-heating type uses a metal ribbon or a metal thread as the thermionic emitter. The metal ribbon or metal thread is fixed between the two electrodes by welding. During use, a voltage is applied between the two electrodes to heat the metal ribbon or metal thread. Kinetic energy of the electrons in the metal ribbon or metal thread is increased. When the kinetic energy of the electrons therein is large enough, thermions will emit or escape from the emitters. The thermionic emitter of the indirect-heating type uses a boride or an alkaline earth metal carbonate as a material of the thermionic emitter. The boride or alkaline earth metal carbonate is dispersed in a conductive slurry, and the conductive slurry is directly coated or sprayed on a heater. The heater can be secured between the two electrodes as a thermionic emitter. During use, a voltage is applied between the two electrodes to heat the thermionic emitter. Kinetic energy of the electrons in the thermionic emitter is increased. When the kinetic energy of the electrons therein is large enough, thermions will emit or escape from the emitters. However, the size of the thermionic emitter using the metal, boride or alkaline earth metal carbonate is large, thereby limiting its application in micro-devices. Furthermore, the coating formed by direct coating or spraying the metal, boride or alkaline earth metal carbonate has a high resistivity, and thus, the thermionic electron source using the same has a greater power consumption and is therefore not suitable for applications involving high current density and brightness.
What is needed, therefore, is a method for making a thermionic electron source having excellent thermal electron emitting properties and wearability, and can be used in flat panel displays with high current density and brightness, logic circuits, and other fields of thermal electron source.